The exemplary embodiments relate to semiconductor devices and, more particularly, to complementary metal oxide semiconductor (CMOS) devices with dual gate dielectrics and dual-metal gate structures and fabrication methods therefor.
Semiconductor devices are used in a variety of electronic applications, such as personal computers, cell phones, digital cameras, and other electronic equipment, as examples. Semiconductor devices are typically fabricated by sequentially depositing insulating (or dielectric) layers, conductive layers, and semiconductive layers of material over a semiconductor substrate, and patterning the various layers using lithography to form circuit components and elements thereon.
A transistor is an element that is utilized extensively in semiconductor devices. There may be millions of transistors on a single integrated circuit (IC), for example. A common type of transistor used in semiconductor device fabrication is a metal oxide semiconductor field effect transistor (MOSFET).
Early MOSFET processes used one type of doping to create either positive or negative channel transistors. More recent designs, referred to as complimentary MOS (CMOS) devices, use both positive and negative channel devices, e.g., a positive channel metal oxide semiconductor (PMOS) transistor and a negative channel metal oxide semiconductor (NMOS) transistor, in complimentary configurations. A PMOS transistor may also be referred to as a PMOSFET or PFET while an NMOS transistor may be referred to as an NMOSFET or NFET. An NMOS device negatively charges so that the transistor is turned on or off by the movement of electrons, whereas a PMOS devices involves the movement of electron vacancies. While the manufacture of CMOS devices requires more manufacturing steps and more transistors, CMOS devices are advantageous because they utilize less power, and the devices may be made smaller and faster.
Dual work function gates are advantageously used in semiconductor devices having both PMOS and NMOS transistors. Some work functions that enable optimal operation of both PMOS and NMOS transistors are required. The optimal work function for a metal gate electrode will differ depending upon whether it is used to form an NMOS transistor or a PMOS transistor. For this reason, when the same material is used to make metal gate electrodes for NMOS and PMOS transistors, the gate electrodes do not demonstrate the desired work function for both types of devices. It may be possible to address this problem by separately forming metal gate electrode of the NMOS transistor from a first material and metal gate electrode of the PMOS transistor from a second material. The first material may ensure an acceptable work function for the NMOS gate electrode, while the second material may ensure an acceptable work function for the PMOS gate electrode.